Impeller pump

ABSTRACT

A centrifugal pump includes a motor with a shaft and an adapter mounted to the motor. A volute housing mounted to the adapter defines a volute chamber. The adapter and volute housing define a pumping chamber therebetween. The volute housing includes an impeller inlet wall having an orifice. An impeller is disposed within the pumping chamber and a hub of the impeller is mounted on the shaft while a shroud portion coincides with the impeller orifice. An inducer is coupled to the shaft and extends into the inlet dogleg. A first portion of the inducer resides within the shroud portion of the impeller and a second portion of the inducer resides within the inlet orifice. The inducer includes helical blades whereby, upon rotation of the shaft, a fluid within the inlet dogleg is acted upon by the helical blades of the inducer before the fluid enters the impeller shroud portion.

FIELD OF THE INVENTION

The present invention relates to impeller-type pumps, such as centrifugal pumps, and more particularly to centrifugal pumps configured to pump fluids near the fluid's vaporization point, and still more particularly to centrifugal pumps including an inducer and impeller to pump a fluid while minimizing the potential for cavitation during pumping operations.

BACKGROUND OF THE INVENTION

Centrifugal pumps utilize an impeller and volute to pump fluids. The impeller, along with other components of the pumping mechanism, may be contained within an adaptor that is connected to a motor. The adaptor is then positioned within a volute housing whereby the impeller is rotated by the motor to move fluid along the volute and out of the volute housing. Specifically, fluid is received through an inlet in the volute housing and is directed to the center of the impeller. The fluid received at the center of the impeller is, during rotation of the impeller, moved outward from the impeller's center. The fluid then leaves the edges of the impeller and is guided by the volute, which directs the flow of fluid through the volute housing.

Cavitation is a phenomenon that occurs when a fluid vaporizes then returns back to a liquid state. This phase change back to a non-compressible liquid state will emit shock waves through the fluid resulting in damage to the closest solid components in the pump or piping. The potential for cavitation to occur in a centrifugal pump system increases as the fluid being pump approaches its vaporization point. One performance characteristic of a centrifugal pump is its NPSHr (net positive suction head required) value. If the net positive suction head available (NPSHa) is lower than NPSHr, cavitation will occur. Thus, to minimize the potential for cavitation, pump designers seek to lower the NPSHr limit. One avenue to achieve the lowest NPSHr for a centrifugal pump application is to include an inducer placed in-line prior to the pump's impeller. Typically, the inducer is attached to the shaft in front of the impeller such that energy is imparted to the fluid by the inducer before the fluid encounters the impeller blades. In this manner, the inlet head may be raised by an amount sufficient to prevent significant cavitation in the impeller pumping stage.

SUMMARY OF THE INVENTION

The present invention has application to impeller-type pumps, such as centrifugal pumps. In general, an aspect of the present invention is directed to a centrifugal pump comprising a motor with a shaft rotatably extending therefrom. An adapter is configured to be mounted to the motor at a first side with the adapter defining an opening for permitting passage of the shaft therethrough. A volute housing is configured to be mounted to a second side of the adapter wherein the volute housing defines a volute chamber and the adapter and volute housing define a pumping chamber therebetween. The volute housing includes an impeller inlet wall delineating the inlet dogleg from the pumping chamber wherein the impeller inlet wall defines an impeller inlet orifice whereby the inlet dogleg is in fluid communication with the pumping chamber. An impeller is configured to be disposed within the pumping chamber such that a hub of the impeller is rotatably mounted on the shaft and the impeller further includes a shroud portion having a wear ring configured to be encompassed by the volute housing and coincide with the impeller inlet orifice. An inducer having an inducer body with a first end is configured to be coupled to a distal end of the shaft. A second end of the inducer body is configured to extend into the inlet dogleg. In this manner, a first portion of the inducer resides within the shroud portion of the impeller and a second portion of the inducer resides within the inlet dogleg. The inducer further includes at least two helical blades extending a length of the inducer from proximate the first end to proximate the second end whereby, upon rotation of the shaft, a fluid within the inlet dogleg is acted upon by the helical blades along the second portion of the inducer before the fluid enters the impeller shroud portion.

In a further aspect of the present invention, each of the helical blades has a variable pitch wherein the pitch decreases linearly from the first end to the second end. In another aspect of the present invention, a leakage flow path is defined between volute housing and the shroud portion of the impeller proximate the impeller inlet orifice. A high pressure leakage flow may then exit the leakage flow path into the volute chamber along the second portion of the inducer.

In still another aspect of the present invention, a centrifugal pump comprises a motor with a shaft rotatably extending therefrom. An adapter is configured to be mounted to the motor at a first side with the adapter defining an opening for permitting passage of the shaft therethrough. A volute housing is configured to be mounted to a second side of the adapter wherein the volute housing defines a volute chamber and the adapter and volute housing define a pumping chamber therebetween. The volute housing includes an impeller inlet wall delineating the inlet dogleg from the pumping chamber wherein the impeller inlet wall defines an impeller inlet orifice whereby the volute chamber is in fluid communication with the pumping chamber. An impeller is configured to be disposed within the pumping chamber such that a hub of the impeller is rotatably mounted on the shaft and the impeller further includes a shroud portion having a wear ring configured to be encompassed by the volute housing and coincide with the impeller inlet orifice. An inducer having an inducer body with a first end is configured to be coupled to a distal end of the shaft. A second end of the inducer body is configured to extend into the volute chamber. In this manner, a first portion of the inducer resides within the shroud portion of the impeller and a second portion of the inducer resides within the inlet dogleg. The inducer further includes at least two helical blades extending a length of the inducer from proximate the first end to proximate the second end. Each of the helical blades may have a variable pitch wherein the pitch decreases linearly from the first end to the second end. Thus, upon rotation of the shaft, a fluid within the volute chamber is acted upon by the helical blades along the second portion of the inducer before the fluid enters the impeller shroud portion. A leakage flow path is defined between volute housing and the shroud portion of the impeller proximate the impeller inlet orifice. A high pressure leakage flow may then exit the leakage flow path into the volute chamber along the second portion of the inducer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a centrifugal pump in accordance with an aspect of the present invention;

FIG. 2 is a partial cross-sectional perspective view of the centrifugal pump of FIG. 1;

FIG. 3 is a partial cross-sectional side view of the centrifugal pump shown in FIG. 1 showing the fluid pathway of a leakage flow;

FIG. 4 is side view of an inducer configured for use within the centrifugal pump shown in FIG. 1; and

FIG. 5 is a plot of blade pitch versus axial distance ratio of the inducer shown in FIG. 4.

DETAILED DESCRIPTION

Referring to FIGS. 1-3, centrifugal pump 10 is shown including motor 12 and volute housing 14 coupled to one another via adapter 16. Shaft 18 may extend from and be rotatably connected to motor 12. Shaft 18 is configured to pass through opening 20 of adapter 16 when adapter 16 is mounted onto motor 12. To that end, adapter 16 may include flanges 17 configured to coincide with and be removably coupled to motor 12 via fasteners 19. Mechanical seal 22 is received within counter bore 24 which defines opening 20. Mechanical seal 22 is then received on shaft 18 by positioning shaft 18 through aperture 26 of mechanical seal 22. By positioning mechanical seal 22 on shaft 18 and within counter bore 24, a fluid tight seal is created between shaft 18 and opening 20 of adapter 16. Adapter 16 is further configured to receive volute housing 14 by coupling with housing sidewall 28 which defines impeller aperture 30. An O-ring 32 may be disposed between adapter 16 and volute housing 14 to create a fluid tight seal therebetween. Volute housing 14 may further include an impeller inlet wall 34 whereby the coupled adapter 16/volute housing 14 defines a pumping chamber 36 therebetween. Pumping chamber 36 receives impeller 38. Impeller inlet wall 34 may further define an impeller inlet orifice 40 such that inlet dogleg 42 is in fluid communication with pumping chamber 36.

As shown in FIGS. 2 and 3, impeller 38 is mounted onto shaft 18 adjacent mechanical seal 22 via hub 39. In accordance with an aspect of the present invention, hub 39 of impeller 38 may include female threads 47 configured to threadably engage corresponding male threads 44 on shaft 18. Impeller 38 may be reverse-threaded such that rotation of shaft 18 does not unwind threads 47 from threads 44 during pump operation. Impeller 38 may further include a shroud portion 46 having a front shroud 48 and wear ring wall 50 whereby a fluid within inlet dogleg 42 may pass through impeller inlet orifice 40 into impeller 38. Shroud portion 46 may also include a plurality of blades 52 that direct the flow of fluid during rotation of impeller 38. Wear ring wall 50 may extend outwardly from front shroud 48 toward impeller inlet orifice 40 and will be discussed in greater detail below.

To minimize, and preferably prevent, the potential for cavitation, pump 10 may further include an inducer 54 having an inducer body 56 with a first end 58 configured to be coupled to distal end 60 of shaft 18. To that end, first end 58 may include female threads 62 configured to threadably mate with male threads 44 on shaft 18. As shown most clearly in FIG. 3, second end 64 of inducer body 56 is configured to extend beyond impeller inlet wall 34 so as to be disposed within inlet dogleg 42. In this manner, a first portion 66 of inducer 54 resides within wear ring wall 50 of impeller 38 while a second portion 68 of inducer 54 resides within inlet dogleg 42. First and second inducer blades 70 extend outwardly from inducer body 56. Each blade 70 may include a helical profile as the blade is defined axially along longitudinal axis L of inducer body 56, and in accordance with an aspect of the present invention, may include a helical profile. Each blade 70 may have a variable pitch as the blade is defined axially and may also vary radially from first end 58 to second end 64. In this manner, the pitch of each blade 70 may decrease at a linear rate from a first end 58 of inducer body 56 to a second end 64. See FIGS. 4 and 5. That is, each blade 70 has a low or shallow pitch proximate second end 64 so as to minimize inception of cavitation. The pitch of each blade 70 may then be increased linearly toward first end 58 so as to create an increased pressure differential per unit axial distance while not causing flow separation of the fluid as it is pumped from inlet dogleg 42 into impeller 38.

Referring again to FIG. 3, front shroud 48 and wear ring wall 50 of shroud portion 46 are configured to be encompassed by volute housing 14 to thereby define a leakage flow path 74 between impeller discharge 76 and volute housing 14 whereby a high pressure leakage flow 76 may exit the leakage flow path 74 into inlet dogleg 42 along the second portion 68 of inducer 54. That is, leakage flow in an enclosed impeller pump system, such as pump 10, is the flow that leaves impeller discharge 76 and passes between the impeller and the volute housing. This leakage flow may be caused by the differential in pressure between the suction region 80 of pump 10 and discharge 76 of impeller 38. As shown in FIG. 3, in accordance with an aspect of the present invention, leakage flow 76 may re-enter suction portion 80 about ⅓ of the axial distance of inducer 54 (from second end 64). Thus, any impeller leakage flow 76 will be directed back into inducer 54 and its flow channel instead of creating reverse or turbulent flow near the entrance of inducer 54. An added benefit is the higher pressure leakage flow from the impeller entering at or near the suction of the inducer, raises the suction pressure which may reduce the chance for the fluid to vaporize at the tip of inducer blades 70. It should be noted that adapter 16, volute housing 14, impeller 38 and inducer 54 may generally comprise an impeller assembly that is configured to mount onto motor 12 and shaft 18 as described above.

While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims. 

What is claimed is:
 1. A centrifugal pump, comprising: a) a motor with a shaft rotatably extending therefrom; b) an adapter configured to be mounted to the motor at a first side, the adapter defining an opening for permitting passage of the shaft therethrough; c) a volute housing configured to be mounted to a second side of the adapter wherein the volute housing defines an inlet dogleg and the adapter and volute housing define a pumping chamber therebetween, wherein the volute housing includes an impeller inlet wall delineating the inlet dogleg from the pumping chamber, wherein the impeller inlet wall defines an impeller inlet orifice whereby the volute chamber is in fluid communication with the pumping chamber; d) an impeller configured to be disposed within the pumping chamber, wherein a hub of the impeller is rotatably mounted on the shaft, and wherein the impeller includes a shroud portion configured to coincide with the impeller inlet orifice; and e) an inducer having an inducer body with a first end configured to be coupled to a distal end of the shaft and a second end configured to extend into the volute chamber, whereby a first portion of the inducer resides within the shroud portion of the impeller and a second portion of the inducer resides within the inlet orifice, wherein the inducer includes at least two helical blades extending a length of the inducer proximate the first end to proximate the second end whereby, upon rotation of the shaft, a fluid within the inlet dogleg is acted upon by the helical blades along the second portion of the inducer before the fluid enters the impeller shroud portion.
 2. The centrifugal pump of claim 1 wherein each of the helical blades has a variable pitch wherein the pitch decreases linearly from the first end to the second end.
 3. The centrifugal pump of claim 1, wherein the shroud portion of the impeller includes a wear ring configured to be encompassed by the volute housing and coincide with the impeller inlet orifice whereby a leakage flow path is defined between volute housing and the wear ring whereby a high pressure leakage flow exits the leakage flow path into the volute chamber along the second portion of the inducer.
 4. A centrifugal pump, comprising: a) a motor with a shaft rotatably extending therefrom; b) an adapter configured to be mounted to the motor at a first side, the adapter defining an opening for permitting passage of the shaft therethrough; c) a volute housing configured to be mounted to a second side of the adapter wherein the volute housing defines a volute chamber and the adapter and volute housing define a pumping chamber therebetween, wherein the volute housing includes an impeller inlet wall delineating the inlet dogleg from the pumping chamber, wherein the impeller inlet wall defines an impeller inlet orifice whereby the inlet dogleg is in fluid communication with the pumping chamber; d) an impeller configured to be disposed within the pumping chamber, wherein a hub of the impeller is rotatably mounted on the shaft, and wherein the impeller includes a shroud portion having a wear ring configured to be encompassed by the volute housing and coincide with the impeller inlet orifice; and e) an inducer having an inducer body with a first end configured to be coupled to a distal end of the shaft and a second end configured to extend into the volute chamber, whereby a first portion of the inducer resides within the shroud portion of the impeller and a second portion of the inducer resides within the inlet orifice, wherein the inducer includes at least two helical blades extending a length of the inducer proximate the first end to proximate the second end, wherein each of the helical blades has a variable pitch wherein the pitch decreases linearly from the first end to the second end whereby, upon rotation of the shaft, a fluid within the volute chamber is acted upon by the helical blades along the second portion of the inducer before the fluid enters the impeller shroud portion, wherein a leakage flow path is defined between volute housing and the wear ring whereby a high pressure leakage flow exits the leakage flow path into the volute chamber along the second portion of the inducer.
 5. An impeller assembly for use within a centrifugal, wherein the centrifugal pump includes a motor with a shaft rotatably extending therefrom, the impeller assembly comprising: a) an adapter configured to be mounted to the motor at a first side, the adapter defining an opening for permitting passage of the shaft therethrough; b) a volute housing configured to be mounted to a second side of the adapter wherein the volute housing defines an inlet dogleg and the adapter and volute housing define a pumping chamber therebetween, wherein the volute housing includes an impeller inlet wall delineating the inlet dogleg from the pumping chamber, wherein the impeller inlet wall defines an impeller inlet orifice whereby the volute chamber is in fluid communication with the pumping chamber; c) an impeller configured to be disposed within the pumping chamber, wherein a hub of the impeller is rotatably mounted on the shaft, and wherein the impeller includes a shroud portion configured to coincide with the impeller inlet orifice; and d) an inducer having an inducer body with a first end configured to be coupled to a distal end of the shaft and a second end configured to extend into the volute chamber, whereby a first portion of the inducer resides within the shroud portion of the impeller and a second portion of the inducer resides within the inlet orifice, wherein the inducer includes at least two helical blades extending a length of the inducer proximate the first end to proximate the second end whereby, upon rotation of the shaft, a fluid within the inlet dogleg is acted upon by the helical blades along the second portion of the inducer before the fluid enters the impeller shroud portion. 